This invention relates to surgical methods generally, and is more specifically related to a method and apparatus for treating intervertebral disks of mammals.
The intervertebral disk is a disk with fibrosus bands occupying the space between two vertebrae. The anatomy of the disk provides a cushion to allow motion, limit motion and provide space, distancing the vertebra off the nerves and compressible tissue. Part of the vertebrae are bony blocks, which, when stacked one upon the other, form the anterior portion of the spine. The fibrosus band includes an outer annulus fibrosus which surrounds an inner nucleus pulposus. Annulus fibrosus, as referred to herein, is the marginal or peripheral portion of an intervertebral disk. Intervertebral disks are prone to injury. Due to the low blood supply to this area, intervertebral disks are slow to heal, and may not materially heal. When the annulus fibrosus is torn, or punctured, the nucleus pulposus can leak or migrate from the annulus fibrosus. The nucleus pulposus is a substance of jelly like consistency found in the center of an intervertebral disk and flows from the associated annulus fibrosus when the annulus fibrosus is ruptured or prolapsed.
The effect of a ruptured or prolapsed annulus fibrosus may result in spasm, and neurological compromise, such as the compressed nerve and other compressible soft tissues, i.e. arteries, veins. Degeneration of the condition may increase over time, resulting in chronic and debilitating pain. The condition is usually disabling.
Suppressive measures include steroidal injection, removal of the nucleus pulposus, and fusion either by donor bone, coral or by metal bracing. If disk removal is performed, a healthy part of the disk is often taken, eradicating the function of the joint, and accelerating the degeneration of adjacent segments of the body, as the body attempts to stabilize. This approach frequently leaves the patient immunologically and structurally compromised if not permanently disabled.
Isolated treatment to only the damaged structures employing the most non-invasive procedure possible is preferred. This approach allows as much of the healthy tissue as possible to remain, and to retain normal neurological function. While the offending material can be removed, the material must be replaced with a material which will perform the function formerly performed by the material removed. A need exists for a process which limits the material removed from the intervertebral disk, and which replaces the material so removed with a composition that is physiologically acceptable to the human body, and which allows the intervertebral disk to retain motion and characteristics of normal joint function, including cushioning the joint as compression is introduced from the stacking of the vertebrae. The thermoplastic material must be pliable in its application, and non-flowing after replacement.
In addition, many patients suffer from scoliosis or lateral curvature of the spine. The most common remedy at the present time is the fusion normally by donor bone or metal bracing which oftentimes is not successful or only partially successful. Pain normally accompanies scoliosis and pain suppressants may result in an undesirable chemical dependency in some instances. A need exists to correct the abnormal curvature of the spine without utilizing fusion techniques applied to the spine.
The present invention is particularly directed to a process for treating the spine including the injection of a thermoplastic material heated to a predetermined temperature for injection into the nucleus pulposus in a flowing state where it cools and sets at body temperature into a non-flowing state. Inorganic materials have been shown to penetrate the endplates of the associated vertebrae. A thermoplastic or thermoplastic polymer material is any plastic or organic material that softens when heated and hardens when cooled. The thermoplastic material prior to injection is heated to a temperature sufficient for the material to flow under pressure into the nucleus pulposus and, after it sets into a non-flowing state at body temperature, the material retains sufficient resilience to provide desired cushioning of the spine.
A thermoplastic material which has been found to be highly satisfactory is gutta percha which is normally combined with other elements or ingredients in a suitable gutta percha compound. Gutta percha is a linear crystalline polymer which melts at a predetermined temperature a random but distinct change in structure results. Normal body temperature is 37 C and a suitable thermoplastic material hardens into a non-flowing state at a temperature range between about 35 C and 42 C (the degree symbol for temperature is omitted in all references herein to a specific temperature). A crystalline phase appears in two forms; an alpha phase and a beta phase. The alpha form is the material that comes from the natural tree product. The processed form is the beta form. When heated, gutta percha undergoes phase transitions. When there is a temperature increase, there is a transition from beta phase to alpha phase at about 46 C. The gutta percha changes to an amorphous phase about 54 C to 60 C. When cooled very slowly, about 1 C per hour, the gutta percha crystallizes to the alpha phase. Normal cooling returns the gutta percha to the beta phase. Gutta percha softens at a temperature above about 64 C. A suitable gutta percha compound is dental gutta percha which contains by weight only about 20% gutta percha with zinc oxide comprising about 60% to 75% of the material. The remaining 5% to 10% consists of various resins, waxes, and metal sulfates. The percentages listed are directed to an optimum gutta percha compound. The preferred percentage of gutta percha is in the range of 15% to 40%. Zinc oxide and metals in the gutta percha compound are desirable for imaging such as X-rays while resins and waxes are desirable for obtaining an adequate flow of the thermoplastic material. Gutta percha provides the desired resiliency at body temperature and is at least about 15% of the compound. Zinc oxide also provides an anti-inflammatory property. In some instances, a mineral trioxide aggregate may be added to the gutta percha compound.
An injection device, such as an injection gun, is utilized for heating and injecting the thermoplastic material under a predetermined pressure within the spine. The injection device may utilize a silver needle, encased in ceramics, of about 20 to 30 centimeters in length with a diameter as high as 1 centimeter. The size of the needle may depend on such factors as the amount of thermoplastic material to be injected, the temperature of the thermoplastic being injected, and the axial pressure applied by the injection device, such as a piston or plunger, to the thermoplastic material to force the heated material from the end of the needle into the spine. The thermoplastic material is physiologically acceptable to the human body.
When the thermoplastic material is utilized to treat a ruptured annulus fibrosus, the nucleus pulposus is removed and the material removed is replaced by the heated thermoplastic material which sets at body temperature and provides sufficient resilience after setting to permit adequate motion and cushioning of the vertebrae. The cushioning effect of the gutta percha compound provides a semimobile disk as a buffer to a fusion to reduce the possibility of sequential iatrogenic disk degeneration. The thermoplastic material is injected within the potential nucleus pulposus space bordered by the annulus fibrosus to replace the removed nucleus pulposus by a needle of the injection device.
When the thermoplastic material is injected within the spine to reduce a scoliosis, the material is sequentially injected by a needle of the injection device into the annulus fibrosus or interannular at the apex and adjacent joints of the concavity of the scoliosis. Such an injection tends to straighten the curvature of the spine is a wedge-like action.
An embodiment illustrated in FIGS. 8-10 includes an injection system in which an expandable member is first expanded into the annulus fibrosus of a disk and then a thermoplastic material is injected into the annulus fibrosus to collapse the expandable member and occupy the space formerly occupied by the expandable member. The expandable member is mounted in concentric relation about the needle.
It is an object of the present invention to provide a method of injecting a thermoplastic material into the annulus fibrosus of a spine.
A further object of the present invention is to provide such a method in which the thermoplastic material is heated to a predetermined temperature for flow into the annulus fibrosus and hardens when it cools from body temperature into a non-flowing state to form a resilient support for cushioning between vertebrae.
Another object of the invention is to provide a method to treat a ruptured annulus fibrosus of a spine by removal of the nucleus pulposus and injection of a thermoplastic material into the annulus fibrosus to replace the nucleus pulposus.
An additional object is to provide an apparatus to treat an annulus fibrosus of a spine in which an injection device heats the thermoplastic material for flow into the annulus fibrosus and another injection member is effective for expanding an expandable member in the annulus fibrosus.
Other objects, features, and advantages of the invention will be apparent from the following specification and drawings.